Fundamental human abilities such as recognizing a loved one, or navigating with a map depend integrally on the extra striate visual cortex. Interestingly, the developmental course of this system is a protracted one, with certain skills continuing to develop into the teenage years. In the adult, higher order visual functions can be divided according to the neuroanatomical subsystems ("what" or ventral occipitotemporal, and "where" or dorsal occipitoparietal) on which they rely. Though a great deal is known regarding these systems in the adult, little is known about the development of these pathways and the emergence of this adult-like dissociation. The proposed studies, therefore, aim to address these uncertainties by utilizing a matched-task paradigm. The "what" task involves perceptual object-matching and the "where" task involves perceptual location-matching; these tasks are matched in that they are identical with respect to stimuli, required response and level of difficulty in adult controls. Study 1 will compare patterns of reaction time performance on these tasks for typical adults and children, with the goal being to explicate developmental changes and examine the emergence of the adult-like behavioral dissociation in what/where processing. Study 2 utilizes functional magnetic resonance imaging (fMRI) to characterize and compare developmental change in the neural substrates underlying "what" and "where" visual processing. Knowledge regarding the relationship between behavioral changes in these systems manifested during development and functional brain activity will allow for the systematic examination of alternative developmental trajectories of these higher order visual functions. Specifically, Study 3 will examine behavioral performance indices and functional brain activity in individuals with congenital/genetic abnormalities (Williams Syndrome) and in individuals who have experienced a prenatal stroke. These populations, thus, afford us the unique opportunity to begin to understand the nature of plasticity and reorganization in these critical perceptual systems. [unreadable] [unreadable]